1. Field of the Invention
The present invention relates to a load driving apparatus, for example, for driving a brake, a heater or the like of a vehicle.
2. Description of the Related Art
In recent years, there has been developed a load driving apparatus which intends to increase a specific fuel consumption and improve a performance by increasing a power supply voltage, for example, supplied to a brake, a heater of the like of a vehicle.
The load driving apparatus is provided with an exclusive controller, and is frequently structured such as to drive a load such as a motor or the like via a switching device, for example, a power supply voltage about 14(V), according to a control signal from the controller. The load driving apparatus mentioned above is structured such as to include a relay circuit as the switching device.
However, in the conventional load driving apparatus, in the case of setting the power supply voltage to a high voltage, for example, about 40(V), there is a problem that the relay circuit widely used as the current switching device can not be used in an appropriating manner. There can be listed a generation of an arc due to a high voltage, a long time of an arc time, a deterioration of contact point within the relay circuit due to the arc, and the like.
Accordingly, there can be considered an improvement of the contact point, a prevention of the arc, an improvement by increasing a gap and the like. However, in this case, there is a problem that it is necessary to use a relay circuit in which they are newly improved, and a much cost is required.
Accordingly, the present invention is proposed by taking the problem mentioned above into consideration, and an object of the present invention is to provide a load driving apparatus which can drive a load with a high voltage by appropriating the conventional load drive as it is.
In order to solve the problem mentioned above, according to the present invention, there is provided a load driving apparatus comprising:
a power source applying a power supply voltage;
a load circuit to which the power supply voltage is supplied from the power source, and driving;
a relay circuit electrically connecting the power source to the load circuit on the basis of a switching operation;
a first switching device driving the relay circuit so as to execute the switching operation;
a second switching device having one end connected to the power source and another end connected to the load circuit, and supplying the power supply voltage to the load circuit; and
a controller outputting a control signal to the second switching device so as to supply the power supply voltage to the load circuit and thereafter outputting a control signal to the first switching device so as to electrically connect the relay circuit to the power source, thereby starting driving the load circuit.
In the load driving apparatus according to the present invention, it is desirable that the controller outputs the control signal to the first switching device so as to cancel the electric connection between the relay circuit and the power source at a time of stopping driving the load circuit after starting driving the load circuit, and thereafter outputs the control signal to the second switching device so as to stop supplying the power to the load circuit.
In the load driving apparatus according to the present invention, the structure may be made such that the controller is provided with a timer counting a predetermined time, supplies the power supply voltage to the load circuit, electrically connects the relay circuit to the power source after the predetermined time counted by the timer elapses, cancels the electric connection between the relay circuit and the power source, and stops supplying the power to the load circuit after the predetermined time counted by the timer elapses.
In the load driving apparatus according to the present invention, the structure may be made such that the controller is provided with a voltage monitor for monitoring a voltage applied to the second switching device, supplies a power supply voltage to the load circuit and electrically connects the relay circuit to the power source after it is judged that the voltage monitored by the voltage monitor becomes greater than a predetermined value.
The structure may be made such that the load driving apparatus according to the present invention is further provided with a rising edge detecting timer circuit inputting an on signal from the controller and outputting an off signal for a predetermined time, an AND circuit to which a control signal from the controller and an output signal from the rising edge detecting timer circuit are input, a falling edge detecting timer circuit outputting an off signal for a predetermined time, and a NAND circuit to which the control signal from the controller and an output signal from the falling edge detecting timer circuit are input, the first switching device switches the relay circuit in response to an output signal from the AND circuit, and the second switching device applies a power supply voltage to the relay circuit in response to an output signal from the NAND circuit.
In order to solve the problem mentioned above, according to the present invention, there is provided a method of driving a load circuit in a load driving apparatus comprising:
a power source applying a power supply voltage;
a load circuit to which the power supply voltage is supplied from the power source, and driving;
a relay circuit electrically connecting the power source to the load circuit on the basis of a switching operation;
a first switching device driving the relay circuit so as to execute the switching operation; and
a second switching device having one end connected to the power source and another end connected to the load circuit, and supplying the power supply voltage to the load circuit, wherein
the method comprises a step of outputting a control signal to the second switching device so as to supply the power supply voltage to the load circuit and thereafter outputting a control signal to the first switching device so as to electrically connect the relay circuit to the power source, thereby starting driving the load circuit.
In the method of driving the load circuit according to the present invention, it is desirable to output the control signal to the first switching device so as to cancel the electric connection between the relay circuit and the power source at a time of stopping driving the load circuit after starting driving the load circuit, and thereafter output the control signal to the second switching device so as to stop supplying the power to the load circuit.
In the method of driving the load circuit according to the present invention, the structure may be made such that the load driving apparatus is provided with a timer counting a predetermined time, supplies the power supply voltage to the load circuit, electrically connects the relay circuit to the power source after the predetermined time counted by the timer elapses, cancels the electric connection between the relay circuit and the power source, and stops supplying the power to the load circuit after the predetermined time counted by the timer elapses.
In the method of driving the load circuit according to the present invention, the structure may be made such that the load driving apparatus is provided with a voltage monitor for monitoring a voltage applied to the second switching device, supplies a power supply voltage to the load circuit and electrically connects the relay circuit to the power source after it is judged that the voltage monitored by the voltage monitor becomes greater than a predetermined value.